On the thermal dissociation of hydrogen

Abstract

The important role atomic hydrogen plays in the low-temperature and pressure deposition of diamond has renewed interest in the dissociation processes of hydrogen. Following a method originally developed by Langmuir and co-workers, the voltage-current characteristics of refractory filaments in vacuum and reduced-pressure gaseous environments are analyzed. Using hydrogen, deuterium, and helium, it is concluded that the difference in the power consumption by the filament in hydrogen and in vacuum is a good measure for the rate of hydrogen dissociation. This rate is shown by experiments and mathematical modeling to depend on the geometry of the refractory heater element. Relatively high dissociation rates, normalized per heater area, are obtained for small-diameter wires, and it is argued that this is indicative of a nonequilibrium dissociation process.

Modeling of the role of atomic hydrogen in heat transfer during hot filament assisted deposition of diamond

“…The observation that the power required to heat the filament to a desired temperature in hydrogen was higher than that in helium is consistent with endothermic dissociation of hydrogen. Higher filament power requirements in hydrogen were also reported in previous investigations 18 '19 . Atomic hydrogen is transported away from the filament primarily by diffusion, as previously established. In the presence of a solid surface, such as the tip of a thermocouple, atomic hydrogen readily recombines to form 8 molecular hydrogen.…”

Low temperature catalytic reactivity of nanodiamond in molecular hydrogen

“…Cond. 1.4 W/m °C at 20°C), is heated at 3300K/ 3027°C in a hydrogen atmosphere [37]. This result strongly suggests that the formation of atomic hydrogen is not only dependent on the temperature but also the contact of hydrogen with the hot refractive filament surface.…”

Hydrogen assisted heat transfer during diamond growth using carbon and tantalum filaments

“…The observation that the power required to heat the filament to a desired temperature in hydrogen was higher than that in helium is consistent with endothermic dissociation of hydrogen at the filament surface 12 . The atomic hydrogen generated at the filament is transported to the substrate primarily by diffusion 13 " 14 .…”